Aqueous cleaning composition containing copper-specific corrosion inhibitor for cleaning inorganic residues on semiconductor substrate

ABSTRACT

A semiconductor wafer cleaning formulation, including 1-21% wt. fluoride source, 20-55% wt. organic amine(s), 0.5-40% wt. nitrogenous component, e.g., a nitrogen-containing carboxylic acid or an imine, 23-50% wt. water, and 0-21% wt. metal chelating agent(s). The formulations are useful to remove residue from wafers following a resist plasma ashing step, such as inorganic residue from semiconductor wafers containing delicate copper interconnecting structures.

RELATED APPLICATIONS

This application is a divisional of and claims the benefit of U.S.application Ser. No. 09/818,073 filed on Mar. 27, 2001 now U.S. Pat. No.6,755,989.

FIELD OF THE INVENTION

The present invention relates generally to chemical formulations usefulin semiconductor manufacturing and particularly to chemical formulationsthat are utilized to remove residue from wafers following a resistplasma ashing step. More specifically, the present invention relates tocleaning formulations for removal of inorganic residue fromsemiconductor wafers containing delicate copper interconnectingstructures.

DESCRIPTION OF THE PRIOR ART

The prior art teaches the utilization of various chemical formulationsto remove residues and clean wafers following a resist ashing step. Someof these prior art chemical formulations include akaline compositionscontaining amines and/or tetraalkyl ammonium hydroxides, water and/orother solvents, and chelating agents. Still other formulations are basedon acidic to neutral solutions containing ammonium fluoride.

The various prior art formulations have drawbacks that include unwantedremoval of metal or insulator layers and the corrosion of desirablemetal layers, particularly copper or copper alloys features. Some priorart formulations employ corrosion inhibiting additives to preventundesirable copper metal corrosion during the cleaning process. However,conventional corrosion-inhibiting additives typically have detrimentaleffects on the cleaning process because such additives interact with theresidue and inhibit dissolution of such residue into the cleaning fluid.Moreover, conventional additives do not easily rinse off the coppersurface after completion of the cleaning process. Such additivestherefore remain on the surface sought to be cleaned, and result incontamination of the integrated circuits. Contamination of theintegrated circuit can adversely increase the electrical resistance ofcontaminated areas and cause unpredictable conducting failure within thecircuit.

The formulation of post CMP cleaners for advanced integrated circuitmanufacturing such as copper and tungsten interconnect materials,includes slurry removal and residue dissolution components thataccelerate the physical cleaning process. However, these conventionaladditives typically have detrimental effects on the metal surface byincreasing resistance and corrosion sensitivity.

It is therefore one object of the present invention to provide chemicalformulations that effectively remove residue following a resist ashingstep, and which do not attack and potentially degrade delicatestructures intended to remain on the wafer.

It is another object of the present invention to replace conventionaladditives with an improved corrosion inhibitor for protection of copperstructures on the semiconductor substrate.

It is another object of the invention to provide an improved corrosioninhibitor, which is easily rinsed off the substrate by water or otherrinse medium after the completion of the residue-removal process,thereby reducing contamination of the integrated circuit.

Other objects and advantages of the invention will become fully apparentfrom the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

The present invention relates generally to chemical formulations usefulin semiconductor manufacturing for removing residue from wafersfollowing a resist plasma ashing step.

In one aspect, the invention relates to a method of removing residuefrom a wafer following a resist plasma ashing step on such wafer,comprising contacting the wafer with a cleaning formulation, including(i) a fluoride source, (ii) at least one organic amine, (iii) anitrogen-containing carboxylic acid or an imine, (iv) water, andoptionally at least one metal chelating agent.

Another aspect of the invention relates to a wafer cleaning formulation,including (i) a fluoride source, (ii) at least one organic amine, (iii)a nitrogen-containing carboxylic acid or an imine, (iv) water, andoptionally at least one metal chelating agent.

In a further aspect, the invention relates to a semiconductor wafercleaning formulation for use in post plasma ashing semiconductorfabrication, comprising the following components in the percentage byweight (based on the total weight of the formulation) ranges shown:

a fluoride source, e.g., ammonium fluoride  1-21% and/or derivative(s)thereof organic amine(s) 20-55% a nitrogenous component selected from0.5-40%  nitrogen-containing carboxylic acids and imines water 23-50%metal chelating agent(s)  0-21% TOTAL 100%

Such formulations of the invention effectively remove inorganic residuesfollowing a plasma ashing step.

Such formulations also effectively remove metal halide and metal oxideresidues following plasma ashing, and effectively remove slurryparticles of aluminum oxides and other oxides remaining after CMP(chemical mechanical polishing).

The formulations of the present invention provide better strippingperformance with less corrosivity than formulations containing eitherammonium fluoride or amines. Formulations in accordance with theinvention also provide better stripping performance at lower processingtemperatures than conventional amine-containing formulations.

The formulations of the invention utilize a chelating agent, which maybe a single-component chelating agent or a multicomponent chelatingagent, to prevent metal corrosion and increase stripping effectiveness.

Other features and advantages of the present invention will be from theensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a copper-specific corrosioninhibitor useful in the broad practice of the present invention, whichforms a protective layer on the copper metal to prevent corrosion;

FIG. 2 is a schematic representation of the copper-specific corrosioninhibitor being rinsed away from the copper surface by deionized water;

FIG. 3 depicts cleaning components of the present invention interactingwith a surface;

FIG. 4 illustrates that formulations of the present invention maybe usedto remove residues and particles;

FIG. 5 provides a SEM representing results obtained from an immersionprocess; and

FIG. 6 illustrates the material etch rate on interconnect materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The formulations of the present invention are suitable for strippinginorganic wafer residues deriving from high density plasma etchingfollowed by ashing with oxygen-containing plasmas. Such formulations arealso suitable for removing slurry particles of aluminum oxides and otheroxides remaining after CMP (chemical mechanical polishing).

The formulations advantageously contain (i) a fluoride source, such asammonium fluoride and/or derivative(s) of ammonium fluoride, (ii) anamine or mixture of amines, (iii) a nitrogen-containing carboxylic acidor imine, (iv) water, and, optionally and preferably, (v) one or moremetal chelating agents.

As used herein, a fluoride source refers to a compound or a mixture ofcompounds that in the aqueous cleaning formulation provides fluorineanions.

The preferred formulations the following components in the percentage byweight (based on the total weight of the formulation) ranges shown:

fluoride source  1-21% organic amine(s) 20-55% a nitrogenous componentselected 0.5-40%  from nitrogen-containing carboxylic acids and imineswater 23-50% metal chelating agent(s)  0-21% TOTAL 100%

The components of the formulation as described above can be of anysuitable type or species, as will be appreciated by those of ordinaryskill in the art. Specific illustrative and preferred formulationcomponents for each of the ingredients of the formulation are describedbelow.

Particular preferred amines include the following:

-   -   diglycolamine (DGA)    -   methyldiethanolamine (MDEA)    -   pentamethyldiethylenetriamine (PMDETA)    -   triethanolamine (TEA)    -   triethylenediamine (TEDA)

Other amines that are highly advantageous include:

-   -   hexamethylenetetramine    -   3,3-iminobis (N,N-dimethylpropylamine)    -   monoethanolamine

Specific preferred fluoride sources include:

-   -   ammonium fluoride    -   triethanolammonium fluoride (TEAF)

Other fluoride sources that are highly advantageous include:

-   -   diglycolammonium fluoride (DGAF)    -   tetramethylammonium fluoride (TMAF)    -   triethylamine tris (hydrogen fluoride) (TREAT-HF)

Specific preferred nitrogen-containing carboxylic acids and iminesinclude:

-   -   iminodiacetic acid    -   glycine    -   nitrilotriacetic acid    -   1,1,3,3-tetramethylguanidine

Other nitrogen-containing carboxylic acids or imines advantageouslyutilizable in formulations of the invention include:

-   -   CH₃C(═NCH₂CH₂OH)CH₂C(O)N(CH₃)₂    -   CH₃C(═NCH₂CH₂OCH₂CH₂OH)CH₂C(O)N(CH₃)₂    -   CH₃C(═NH)CH₂C(O)CH₃    -   (CH₃CH₂)₂NC(═NH)N(CH₃CH₂)₂    -   HOOCCH₂N(CH₃)₂    -   HOOCCH₂N(CH₃)CH₂COOH

Specific preferred metal chelating agents include:

-   -   acetoacetamide    -   ammonium carbamate    -   ammonium pyrrolidinedithiocarbamate (APDC)    -   dimethyl malonate    -   methyl acetoacetate    -   N-methyl acetoacetamide    -   2,4-pentanedione    -   tetramethylammonium thiobenzoate    -   tetramethylammonium trifluoroacetate    -   tetramethylthiuram disulfide (TMTDS)

The combination of ammonium fluoride or a substituted fluoride source,as described above, with an amine (other than an amine present as asurfactant in an amount of 1% or less) provides better strippingperformance with less corrosivity than formulations containing eitherammonium fluoride or amines alone. In addition, the resulting alkalinesolutions are effective at lower processing temperatures (e.g., 21°-40°C.) than conventional amine-containing formulations.

The presence of nitrogen-containing carboxylic acids and/or iminesenables formulations of the invention to be remarkably effective instripping residues from semiconductor substrate surfaces containingdelicate copper structures.

The nitrogen-containing carboxylic acids or imines provide functionalgroups that are specifically attracted to free copper atoms. As shownschematically in FIG. 1, the copper-specific corrosion inhibiting-agentC, while contacts the copper surface during the residue-removal process,will attach to the copper surface and form a protective layer to preventthe copper surface being corroded by cleaning agents A⁺ and X⁻.

Moreover, as shown by FIG. 2, such copper-specific corrosion-inhibitingagent C can be easily rinsed off by deionized water or other solutionsand therefore leaves very little contamination on the copper surfaceafter the cleaning operation.

The use of 1,3-dicarbonyl compounds as chelating agents and to preventmetal corrosion is a preferred feature of the inventive formulations, toincrease their effectiveness.

In various prior art formulations, amines are present in amounts of 1%or less of the formulation as surfactants, or otherwise are not utilizedas formulation ingredients at all. Additionally, the prior artformulations are acidic (pH<7) in character. In preferred formulationsof the present invention, the amines are present as major components ofthe formulation, are highly effective in stripping action, and yieldformulations of a basic pH character (pH>7).

The formulations of the invention may include a wide variety of organicamines, substituted ammonium fluorides, and nitrogen-containingcarboxylic acids, other than those specifically exemplified. Particularsubstituted ammonium fluorides of suitable character include those ofthe general formula, R₁R₂R₃R₄NF in which each of the respective Rspecies is independently selected from hydrogen and aliphatic groups.Suitable nitrogen-containing carboxylic acids include those of thegeneral structure COOH—CH₂—NRR′, wherein R and R′ are each independentlyselected from the group consisting of hydrogen, alkyl, aryl, andcarboxylic acid moieties. Suitable metal chelating agents include1,3-dicarbonyl compounds of the general structure X—CHR—Y. In compoundsof such formula, R is either a hydrogen atom or an aliphatic group,e.g., C₁-C₈ alkyl, aryl, alkenyl, etc. X and Y may be the same as ordifferent from one another, and are functional groups containingmultiply-bonded moieties with electron-withdrawing properties, as forexample CONH₂, CONHR′, CN, NO₂, SOR′, or SO₂Z, in which R′ represents aC₁-C₈ alkyl group and Z represents another atom or group, e.g.,hydrogen, halo or C₁-C₈ alkyl.

Other chelating agent species useful in the compositions of theinvention include amine trifluoroacetates of the general formula,R₁R₂R₃R₄N⁺⁻O₂CCF₃ in which each of the R group independently selectedfrom hydrogen and aliphatic groups, e.g., C₁-C₈ alkyl, aryl, alkenyl,etc.

The formulations of the invention optionally may also include suchcomponents as surfactants, stabilizers, corrosion inhibitors, bufferingagents, and co-solvents, as useful or desired in a given end useapplication of formulations of the invention.

Formulations in accordance with the present invention are particularlyuseful on wafers that have been etched with chlorine- orfluorine-containing plasmas, followed by oxygen plasma ashing. Theresidues generated by this type of processing typically contain metaloxides. Such residues are often difficult to dissolve completely withoutcausing corrosion of metal and titanium nitride features required foreffective device performance. Also, metal oxide and silicon oxide slurryparticles remaining after CMP will also be effectively removed byformulations in accordance with the present invention.

The features and advantages of the invention are more fully shown by thefollowing non-limiting examples.

EXAMPLE 1

Copper-specific corrosion inhibitors including eitherhydrogen-containing carboxylic acids or imines were tested in twodifferent types of alkaline cleaning formulations, with the followingcomponents and characteristics.

TABLE 1 Copper Etch Temp., Rate Components ° C. pH (Å/min) Formulation 1dimethylacetoacetamide, 70 6.2 17.4 amine, and water Formulation 2ammonium fluoride, 40 8.6  7.5 triethanolamine,pentamethdiethylenetriamine, and water

The copper etch rate was determined by a standard four-point probetechnique. Addition of corrosion inhibitors in accordance with thepresent invention significantly slowed down the copper etch rate, asshown by the following table, and effectively prevented undesirablecorrosion during the cleaning process:

TABLE 2 Copper Etch Reduction of Temp. Formulation Concentration pH ofRate Etch Rate Corrosion Inhibitor (° C.) Used (%) solution (Å/min) (%)Iminodiacetic Acid 40 2 1.5 8.0 1-2 −73.3˜86.7 Glycine 40 2 1.5 9.2 3.6−52.0 Nitrilotriacetic Acid 40 2 1.5 8.2 3.6 −52.01,1,3,3-tetramethylguanidine 40 2 1.5 8.7 3.4 −54.7CH₃C(═NCH₂CH₂OH)CH₂C(O)N(CH₃)₂ 70 1 24 10.9 6.2 −64.4CH₃C(═NCH₂CH₂OCH₂CH₂OH)CH₂C(O)N(CH₃)₂ 70 1 36 10.7 0.32 −98.2CH₃C(═NH)CH₂C(O)CH₃ 40 2 13.68 7.9 4.4 −41.3

EXAMPLE 2

A contamination test was carried out on Formulation 2 containingiminodiacetic acid inhibitor. The semiconductor wafer to be cleanedcontained copper and silicon films. After the completion of the cleaningoperation, the wafer was rinsed by deionized water at 25° C. for about15 minutes. The Secondary Ion Mass Spectrometry data (SIMS) obtained areas follows:

Cu (atoms/cm²) F (atoms/cm²) C (atoms/cm²) Cu_(x)O (Å) Uncleaned  1.6 ×10¹⁰ 3.3 × 10¹³ 7.5 × 10¹³ 42 Wafer Cleaned 8.5 × 10⁹ 5.1 × 10¹³ 1.5 ×10¹³ 15 WaferThe foregoing results show that the copper oxide Cu_(x)O has beeneffectively removed by the cleaning process, while carbon contamination,which is mainly caused by the organic corrosion inhibitors in thecleaning formulation, has been greatly reduced.

The present invention employs dilute alkaline fluoride in compositionsfor post CMP cleaning of silicon oxide or aluminum oxide particles frommetallic surfaces such as copper or tungsten. FIG. 3 depicts how thecleaning components of the present invention interact with the surface.Specially, FIG. 3 depicts that Alkaline Fluoride 30 and chelating agents32 dissolving inorganic oxide residues 34 after a CMP process.

FIG. 4 illustrates that the formulations taught by the present inventionmay be used to remove residues 40 and particles 42 for a copper surface44. In FIG. 4 particles 42 and residues 40 adhere to metal surface 44 aswell as dielectric surface 46. Particles 42 and residues 40 may remainfollowing a CMP process. The chemical solutions of the present inventiondegrade the attractive forces between the residue and the surface aswell as dissolve copper and tungsten oxides and oxy-halides.

Formulations that have been found to be effective in cleaning residueand slurry particles from metal surfaces typically have pH valuesbetween about 7 and about 9. These formulations generally are aqueoussolutions that comprise a fluoride source, an organic amine, and metalchelating agent. The individual constituents typically constitute afluoride source and/or a derivative thereof as about 0.1 to about 4.2%of the formulation. The fluoride source may include Ammonium Fluoride,Triethanolammonium Fluoride (TEAF), Diglycolammonium Fluoride (DGAF),Tetramethylammonium Fluoride (TMAF), Ammonium Bifluoride or other suchfluoride sources as known to those skilled in the art. The organic Amineor mixture of two amines typically comprises between about 2% and about11% of the formulation of the present invention, wherein the organicamine can be one of many such organic amines known to those skilled inthe art including Methydiethanolamine, Pentamethydiethylenediamine(PMDETA), Triethanolamine (TEA), Monoethanolamine, and Diglycolamine.The metal chelating agent or mixture of chelating agents typicallycomprises about 0 to about 4.2% of the formulation. Typical metalchelating agent include: iminodiacetic acid, 2,4-pentanedione,methyldiethanolammonium trifluoroacetate, ammonium carbamate, ammoniumpyrrolidinedithiocarbamate, ammonium lactate, malonic acid or othersimilar agents as known to those skilled in the art.

Several representative examples of formulations are:

a. Triethanolamine  4.5%     Ammonium Fluoride  0.5%     Water   95% b.PMDETA 3.8-4.5%    Ammonium Fluoride  0.5%    2,4-Pentanedione    1%   Water   94-94.7% c. TEA  1.7%     PMDETA  1.5%     TEAHF    2%    Iminodiacetic Acid  0.4%     Ammonium Bifluoride  0.5%     Water  93.9%d. TEA  3.5%    PMDETA  1.5%    2,4-Pentanedione  1.35%    AmmoniumFluoride  1.2%    Water 92.45% e. TEA    7%     PMDETA    3%    2,4-Pentanedione  2.7%     Ammonium Fluoride  2.4%     Water  84.9%

Wafers can be immersed in chemical solutions or chemicals can be appliedto the wafer surface by spray or through a brush scrubbing system. FIG.5 depicts a SEM representing the results obtained with a standardimmersion process. Specifically FIG. 5 depicts Tungsten plugs afteralumina slurry CMP and immersion in formula c for 10 min at 30 ° C.Furthermore, selectivity to exposed materials may be illustrated by etchrate data. FIG. 6 and table 3 illustrate the material etch rate oninterconnect materials including an electroplated copper film.

TABLE 3 Etch Rate, Å/min for 21° C. Material @ 30 min Copper ˜1 TantalumNitride <0.1 Titanium <0.1 Titanium Nitride 1.0 Tungsten 0.2 TEOS 1.5BPSG 4.5

While the invention has been described herein with reference to specificfeatures, aspects, and embodiments, it will be appreciated that theinvention is not thus limited. The invention therefore maycorrespondingly embodied in a wide variety of compositions, withcorresponding variations of ingredients, and end use applications. Theinvention therefore is to be understood as encompassing all suchvariations, modifications and alternative embodiments, within the spiritand scope of the invention as hereafter claimed.

1. A method for fabricating a semiconductor wafer, comprising: plasmaetching a metalized layer from a surface of the wafer; plasma ashing aresist from the surface of the wafer; cleaning the wafer by contactingsame with a cleaning formulation, comprising, by weight between about 1%and about 21% fluoride source, between about 20% and about 55% organicamino, between about 23% and about 50% water, a metal chelating agentand between about 0.5% and about 40% of a nitronenous componentincluding a compound of the formula COOH-CH₂-NRR′, wherein each of R andR′ is independently selected from the group consisting of hydrogen,alkyl, aryl and carboxylic acids.
 2. The method of claim 1, wherein saidfluoride source comprises a fluoride species selected from the groupconsisting of: animonium fluoride; and triethanolammnonium fluoride(TEAF).
 3. The method of claim 1, wherein said organic amine(s) comprisean amine selected from the group consisting of: diglycolamine (DGA),methyldiethanolamine (MDEA), pentamethyldiethylenetriamine (PMDETA),triethanolamine (TEA), and triethylenediamine (TEDA).
 4. The method ofclaim 1 wherein said nitrogenous component comprises a species selectedfrom the group consisting of: iminodiacetic acid (IDA); glycine;nitrilotriacetic acid (NTA); and 1,3,3-tetramethylguanidine (TMG). 5.The method of claim 1, including at least one metal chelating agentselected from the group consisting of: acetoacetamide, ammoniumcarbamate, ammonium pyrrolidinedithiocarbamate (APDC), dimethylmalonate, methyl acetoacetate, N-methyl acetoacetamide,2,4-pentanedione, tetramethylammoniuim thiobenzoate, tetramethylammoniumtrifluoroacetate, and tetramethylthiuram disulfide (TMTDS).
 6. Themethod of claim 1 wherein said fluoride source comprises a speciesselected from the group consisting of: ammonium fluoride,triethanolammonium fluoride (TEAF), diglycolammonium fluoride (DGAF),tetramethylamnmonium fluoride (TMAF), and triethylamine tris (hydrogenfluoride) (TREAT-HF).
 7. The method of claim 1 wherein said organicamine(s) comprises an amine selected from the group consisting of:diglycolamine (DGA), methyldiethanolamine (MDEA),pentamethyldiethylenetriamine (PMDETA), triethanolamine (TEA),triethylenediamine (TEDA), hexamethylenetetramine, 3,3-iminobis(N,N-dimethylpropylamine), and monoethanolamine.
 8. The method of claim1 wherein said nitrogenous component comprises a species from the groupconsisting of: iminodiacetic acid (IDA); glycine; nitrilotriacetic acid(NTA); 1,1,3,-tetramethylguanidine (TMG);CH₃C(═NCH₂CH₂OH)CH₂C(O)N(CH₃)₂; CH₃C(═NCH₂CH₂OCH₂CH₂OH)CH₂C(O)N(CH₃)₂.CH₃C(═NH)CH₂C(O)CH₃; (CH₃CH₂)₂NC(═NH)N(CH₃CH₂)₂; HOOCH₂N(CH₃)₂; andHOOCCH₂N(CH₃)CH₂COOH.
 9. The method of claim 1 wherein said fluoridesource comprises a species selected from the group consisting of:ammonium fluoride, triethanolammonium fluoride (TEAF), diglycolammoniumfluoride (DGAF), tetramethylammonium fluoride (TMAF), and triethylaminetris (hydrogen fluoride) (TREAT-HF); said organic amine(s) comprise aspecies selected from the group consisting of: diglycolamine (DGA),methyldiethanolamine (MDEA), pentamethyldiethylenetriamine (PMDETA),triethanolamine (TEA), triethylenediamine (TEDA),hexamethylenetetramine, 3,3-iminobis (N,N-dimethylpropylamine), andmonoethanolamine; said nitrogenous component comprises a speciesselected from the group consisting of: iminodiacetic acid (IDA),glycine, nitrilotriacetic acid (NTA), 1,1,3,3-tetramethylguanidine(TMG); and said formulation includes a metal chelating agent comprisinga species selected from the group consisting of: acetoacetamide,ammonium carbamate, ammonium pyrrolidinedithiocarbamate (APDC), dimethylmalonate, methyl acetoacetate, N-methyl acetoacetamide,2,4-pentanedione, tetramethylammonium thiobenzoate, tetramethylammoniumtrifluoroacetate, and tetramethylthiuram disulfide (TMTDS).
 10. Themethod of claim 1 wherein said fluoride source comprises a compoundhaving the general formula R₁R₂R₃R₄NF in which each of the R groups isindependently selected from hydrogen atoms and aliphatic groups, andwherein said formulation includes a metal chelating agent of theformula: X-CHR-Y, in which R is either hydrogen or an aliphatic groupand X and Y are functional groups containing multiply bonded moietieshaving electron-withdrawing properties.
 11. The method of claim 10wherein each of X and Y is independently selected from CONH₂, CONHR′,CN, NO₂, SOR′, and SO₂Z in which R′ is alkyl and Z is hydrogen, halo, oralkyl.
 12. The method of claim 1 wherein said fluoride source comprisesa compound having the formula R₁R₂R₃R₄NF in which each of the R groupsis hydrogen or aliphatic, and wherein said formulation includes a metalchelating agent of the formula, R₁R₂R₃R₄N⁺⁻O₂CCF₃ in which each of the Rgroups is independently hydrogen or aliphatic.
 13. The method of claim1, wherein the cleaning formulation comprises by weight between about 1%and about 21 % metal chelating agent.